Characteristic antibodies which react with normal tissues (autoantibodies) develop in patients with a number of diseases and in some animals. Considerable evidence suggests that some of these antibodies arise because of specific interactions between an exogenous agent (virus, bacterium, drug) and the sites to which the antibody binds. A search is underway to determine whether certain picornaviridiae can be implicated in the causation of inflammatory myositis and the characteristic myositis related antibodies which react with amino acid t-RNA synthetases.